In electronic transformers which have an active power factor correction circuit the choice of intermediate circuit voltage is of great significance with regard to functionality and costs. These transformers are usually constructed as simple step-up converters without galvanic isolation (known as flyback topology). They are usually operated at the ripple limit, that is to say between rippled operation and ripple-free operation. There is the problem that, with barely adequate, low-cost component dimensioning, a specific value of the intermediate circuit voltage must not be exceeded, since otherwise components such as the intermediate circuit capacitor may be overloaded and suffer permanent damage. If there is a slightly increased input voltage, the transformer can still keep the intermediate circuit voltage constant by appropriate activation of the switch. If the input voltage increases greatly, for example as a result of a fault in the power supply system, the transformer can no longer correct the intermediate circuit voltage, and the intermediate circuit voltage increases. This puts a load on components such as, for example, the intermediate circuit capacitor. If the electrical transformer is operated with a load that is not continuous over time, the intermediate circuit capacitor is subjected to a voltage and current ripple in addition to the increased intermediate voltage. In many cases, this overloads the component, so that irreversible damage to the component is not ruled out. Therefore, an overvoltage disconnection is often implemented in such transformers. Suitable disconnection criteria allow the component loadings, in particular the current and voltage loading, of the intermediate circuit capacitor under abnormal operating conditions to be reduced. In the case of electrical transformers according to the prior art, the mean value of the intermediate circuit voltage is detected. As already mentioned above, this voltage is of course the output voltage of the electrical transformer. If, as a consequence of an increased input voltage that can no longer be corrected by the electrical transformer, the mean value of this voltage exceeds a value of 109% of the nominal value, the entire device including the load is disconnected. For this purpose, it is necessary that the load is disconnectable. In many applications, such as for example in the case of an electronic operating device for gas discharge lamps, this is no problem, since the transformer is followed by an inverter, which operates the actual load, a gas discharge lamp. This inverter can easily be disconnected in order to protect the entire operating device from the excessive input voltage. Disconnecting the load does not cause any ripple current or ripple voltage, which protects the components of the transformer, in particular the intermediate circuit capacitor. The problem of this known disconnection is that it only takes effect very late, and the components consequently cannot be dimensioned to a desired low value. For example, for applications with the supply voltage customary in Europe of 230 V AC, the known disconnection only takes effect when there is an input AC voltage of 340 V. This represents high loading for many components of the transformer.